1. Field of the Invention
The present invention relates to a current detection circuit, and a motor driving device, a magnetic disk storage device, and an electronic appliance using the current detection circuit.
2. Description of Related Art
Conventionally, there is used a motor driving device for driving a motor using a voltage supplied to a power supply line. Such a motor driving device includes, for example, a switch for switching connection/disconnection between each phase of the motor and the power supply line and a switch for switching connection/disconnection between each phase of the motor and a ground point. When these switching of the switches are performed appropriately, the motor can be driven.
Note that there is a PCT publication WO2009/150794 as a related art of the present invention.
Here, if a maximum current in the motor (that means current of a maximum value among currents flowing in phases in this specification) is too large, it is necessary to perform an operation for securing safety of the device, for example. Therefore, the motor driving device is required to have a function of detecting a maximum current value (that means a value of the maximum current). With this function, the motor driving device can perform the operation when the maximum current value exceeds a predetermined threshold value, for example.
However, it may be difficult to directly detect the maximum current value depending on a direction of the maximum current in the motor. For instance, when brake control of a three-phase motor having an A-phase, a B-phase, and a C-phase is performed (when low side FETs of all phases are turned on), if current flows from the A-phase to the B-phase and the C-phase, current flowing in the path from the ground point to the motor via the low side FET of the A-phase becomes the maximum current. In this case, a terminal voltage of the A-phase becomes a negative voltage, and a parasitic diode of the switch may operate. In this case, it is not easy to directly detect the maximum current value.